Forbes is questioning the efficiency of the Apple supply chain now that Tim Cook is running the company and not just the supply chain and operations. I think this is a bit of a stretch and also a bit of hype as everyone tries to find issues with the leader. I doubt very much if anything substantively has improved or devolved since Tim Cook took over the entire company - things don't "rust" that fast.
The future will tell however I would hate to be part of the millions of people who have counted Apple down for the count more than once. It is a great company and will be for quite some time.